Microsoft said on Wednesday that its Xbox 360 has become the first next-generation video game console to hit 10 million units sold in the United States.

Further, said Aaron Greenberg, director of product management for Xbox 360 and Xbox Live, that milestone has historically been reached by the eventual best-seller of each previous console generation, a fact that Microsoft will certainly be using to bolster suggestions that the Xbox 360 will eventually prevail sales-wise over Nintendo's Wii and Sony's PlayStation 3.

Of course, Sony has been the winner of the two previous generations, with the original PlayStation and PlayStation 2 far outselling the competition.

In the U.S., according to NPD Group analyst Anita Frazier--as of the end of March, Microsoft's rivals, Nintendo, and Sony had sold 8.8 million Wiis and 4.1 million PlayStation 3's in the United States, respectively.

All told, Microsoft has sold 19 million Xboxes worldwide, Greenberg said.

In addition, he reported that globally, Microsoft's Xbox Live service has reached 12 million total users, more than doubling the 6 million it reported last July.

"Our goal was to hit 10 million (Xbox Live users) in a year's time," Greenberg said, "and we've doubled it in less time. The majority of Xbox owners on a global basis are connecting to Xbox Live."

Another milestone the Xbox recently reached, Greenberg said, was that with more than 1 million copies of Rockstar Games' monster hit, Grand Theft Auto IV, having already sold on Xbox 360, the console has now reached 16 different titles with 1 million sales or more in the U.S.

By comparison, he pointed out, that's twice the number of million-plus titles that have sold for the Wii in the U.S. The PlayStation 3 has had just two, he said.

While the 10 million total Xboxes sold in the United States is certainly notable, it also must be noted that the console had a full year's head start on its competition.

Greenberg acknowledged that that means it's hard to compare sales numbers in an apples-to-apples fashion, but added that he thinks the head start gives Microsoft advantages that Sony and Nintendo will never be able to catch up to.

"I don't think you can underestimate the benefit of the year head start," he said. "We have a larger library, a larger online community. There's benefits to that acceleration."

Additionally, because the Xbox has been on the market a year longer, Microsoft has been able to reduce the costs of production sooner than its rivals, Greenberg said.

"It's hard to play catch-up," he said.

More recently, Greenberg explained, the huge success of GTA IV has been a boon to the Xbox. He explained that Microsoft's initial data suggested that in the first week the game was on the market, fully 40 percent of Xboxes sold at retail were bought by people who also purchased GTA IV.

That certainly seems like good news for Microsoft and backs up suggestions by industry analysts who predicted that GTA IV would drive a significant number of sales of the Xbox 360 and the PlayStation 3, the two consoles the game was released on.

On Thursday, NPD will release its April sales figures for the U.S. video game industry.

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